Oscilloscopes utilizing video signals to modulate the beam with varying deflection periods

ABSTRACT

An oscilloscope is disclosed which includes means for producing deflection of the beam of a cathode-ray tube in one direction at a relatively high frequency and deflection in another direction at a lower frequency, means for gating video signals to modulate said beam during a short interval in each of a series of lower frequency deflection periods, the timing of said short intervals being changed in successive periods so that the waveform of said video signals is displayed. There is also disclosed as a further feature means for gating signals to form one or more markers on the display during respective selected high-frequency deflection periods in each lower frequency deflection period.

United States Patent Talbert 51 Mar. 7, 1972 54] OSCILLOSCOPES UTILIZING VIDEO 3,395,310 7/1968 Zuuren .3|5/22 SIGNALS o MODULATE THE BEAM 2,858,475 10/1958 Blake ...315/22 x WITH VARYING DEFLECTION PERIODS Wu et al.

Primary ExaminerRodney D. Bennett, Jr.

72 lnventor: David Godwin Talbert, London, England 14mm"! Examiner-l Polenm Attorney-William W. Downing, Jr. [73] Assigneez S.E. Laboratories (Holdings) Limited,

Feltham, Middlesex, England [57] ABSTRACT l22l lv l 1- T 1 9 An oscilloscope is disclosed which includes means for producing deflection of the beam of a cathoderay tube in one [2| 1 Appl' 865252 direction at a relatively high frequency and deflection in another direction at a lower frequency, means for gating video [30] Foreign Application Priority Data signals to modulate said beam during a short interval in each of a series of lower frequency deflection periods, the timing of Oct. 1 l, 1968 Great Britain ..48,373/ 68 said short intervals being changed in successive periods so hat the waveform of said video signals is displayed. There is also U-S. di closed as a further feature means for gating igna's to form [51] d 8 1 29/70 one or more markers on the display during respective selected [58] Field of Search ..315/22, 30, 26 hi h-f d fl tion eriod in each lower frequency deflection period. [56] References Cited 6 Claims, 1 Drawing Figure UNITED STATES PATENTS 2,840,756 6/1958 Reeves ..315/22 MOOO TO l.A R REFERENCE COMPARATOR GATE 12 11 13 COMPARATOR GATE 3 3 1 2 1 14 15 9 A i h i N 4 I I-I SIGNAL I COMPARATOR GATE SHIFT l 1 l l I 1 I 1 5n l i SIGNAL COMPARATOR OATE SHTF T n Patented March 7, 1972 TO MODULATOR COMPARATOR GATE COMPARATOR BATE REFERENCE COMPARATOR GATE SIGNAL 1 SHIFT 1 COMPARATOR OATE SIGNAL n SHTFTn OSCILLOSCOPES UTILIZING VIDEO SIGNALS T MODULATE THE BEAM WITH VARYING DEFLECTION PERIODS This invention relates to oscilloscopes.

It has been proposed hitherto to provide an oscilloscope including a deflection circuit which provides a vertical deflecting waveform of high frequency and a horizontal deflecting waveform of relatively low frequency. Means are also provided for generating a sawtooth voltage, called a ramp, synchronous with the vertical deflecting waveform so that its instantaneous value corresponds to the vertical deflecting waveform and therefore corresponds to the vertical deflection of the beam on the screen. A plurality of signals to be displayed are compared with the ramp, the signals being superimposed respectively on progressively higher direct shift voltages, which are separated by amounts exceeding the maximum amplitude of the respective signal. During each cycle of the ramp, successive coincidences occur between the ramp and the signals superimposed on the respective shift voltages and each time a coincidence occurs a bright-up signal is generated which is applied to the beam of the cathode-ray tube to produce a bright spot on the screen. The vertical deflection frequency is high enough for each signal to be displayed as a substantially continuous trace. On the other hand the period of the horizontal deflecting waveform is sufficiently long to allow for the display of slowly varying waveforms. The horizontal deflection period may be between 0.1 second and seconds to suit the rate of variation of the signals to be displayed.

In some applications of such oscilloscopes it may also be desired to display fixed information such as range markers, medical average parameters, oil pressures and the like. However difficulty is encountered because the decay time of the phosphor is such that information written at the start of one horizontal deflection period has faded by the end of the period.

An object of the present invention is to provide an improved oscilloscope adapted for displaying slowly varying waveforms.

A further object of the present invention is to provide an improved oscilloscope adapted for displaying markers superimposed on slowly varying waveforms.

According to the present invention there is provided an oscilloscope including a. means for producing deflection of the beam of a cathoderay tube in a first direction at a first frequency,

b. means for producing deflection of said beam in an orthogonal direction to said first direction at a second frequency which is low relative to said first frequency,

c. means for defining an interval in each second frequency deflection period, the timing of the occurrence of the interval being changed in successive second frequency deflection periods, and

d. gating means for allowing at least one signal to intensity modulate said beam only during said intervals whereby the waveform of said signal is displayed on the display of said cathode-ray tube.

According to a feature of the present invention there is provided an oscilloscope in accordance with the preceding paragraph including further gating means for gating further signals to form a marker on the display during a selected first frequency deflection period in each second frequency deflection period.

In order that the present invention may be clearly understood and readily carried into effect it will now be described with reference to the single FIGURE of the accompanying drawings which illustrates in block form part of an oscilloscope according to one example of the invention.

Referring to the drawing, the oscilloscope which is illustrated includes a cathode-ray tube 1, which is shown symbolically in sectional view. The tube has vertical deflecting plates 2 and horizontal deflecting plates 3. Alternatively plates 2 and 3 may be replaced by vertical and vertical magnetic deflection coils. The horizontal deflecting plates 2 receive a sawtooth waveform of relatively high frequency from a circuit 4 and a corresponding waveform is also fed, to act as a ramp, to a series of comparison circuits two of which are denoted by the references S and 5,, The comparison circuits 5, 5, receive, as second input signals, signals to be displayed superimposed on successively larger direct shift voltages. Two of the circuits for superimposing a signal on a respective shift voltage are denoted by the references 6, and l5, and, in known manner, the shift voltages may be arranged to be separated by amounts exceeding the maximum amplitudes of the respective signals. Each time one of the comparison circuits 5 5 detects coincidence between the two signals applied to it, it produces an output gating pulse which opens the respective one of the gates 7, 7, from which is generated a respective bright up signal via a transistor switch. Because of the DC shifts, superimposed on the signals, the gates 7 7,, are opened successively for short periods during each ramp period, that is during each vertical deflection period, and each gate generates a'short bright-up pulse which is capable of producing a bright spot on the screen of the cathode-ray tube 1. However in this example of the invention these bright-up pulses are not applied directly to the modulator electrode of the cathode ray tube but are fed to another gate 9, the operation of which willbe described subsequently.

The horizontal deflecting waveform which is applied to the plates 3 of the cathode-ray tube is of relatively short deflection period compared with the periods proposed above, say onefiftieth of a second. The horizontal deflecting sawtooth waveform is generated by a circuit 10 and this circuit is also arranged to provide a corresponding ramp voltage of 50 cycles per second to a comparison circuit 11. The second input to this comparison circuit is a reference voltage derived from a circuit 12. ln this example of the invention the reference is a fixed voltage which is however capable of manual adjustment. When the circuit 11 detects coincidences between the ramp from the circuit 10 and the reference voltage from the circuit 12 it applies an output signal to a gate 13 to open the gate from which is generated a bright-up signal as long as the signal from circuit 11 is present which is applied to the modulator of the cathode-ray tube 1. The comparison circuit 11 is arranged to produce an output signal which lasts for a vertical deflection period, and to this end circuit 11 may include a monostable circuit triggered in response to the detection of a coincidence to produce a pulse of duration equal to a vertical deflection period. The operation of the comparison circuit 11 and the gate 13 is to cause a substantially vertical marker line to be displayed by the cathode-ray tube at a selected horizontal position, the line being regenerated in each period of the waveform from the circuit 10. Because the period of the latter waveform is relatively short, as described above, the marker line so produced is not susceptible to fading.

The period of the waveform derived from the circuit 10 is however now insufficiently long for displaying the slowly moving waveforms corresponding to the video signals applied to the comparison circuits 5 5,. Therefore a further sawtooth waveform generator 14 is provided which generates a ramp voltage of relatively long period, and which is comparable with the period of the horizontal deflection waveform of prior art oscilloscopes. The ramp from 14 is compared in a comparison circuit 15 with the ramp from the circuit 10, and on the assumption that the two ramps are of the same amplitude the circuit 15 will detect coincidences between the two waveforms once in every period of the ramp from circuit 10. However the coincidences will occur at successively later times in successive periods of the ramp from circuit 10. Therefore the coincidences will be detected during sequentially occurring periods of the vertical deflecting waveforms generated by the circuit 4. The comparison circuit 15 is arranged to produce a gating waveform lasting for one vertical deflection period and thiswaveforrn is applied to the gate 9 to allow the bright-up pulses from the gates 7, 7, to be applied to the modulator electrode of the cathode ray tube 1. Therefore, the period allowedfor the formation of the slowly varying waveforms corresponding to the video signals is the period of the waveform generated by the circuit 14.

lt will be appreciated that more than one marker may be produced at the display by providing more than one source, such as 12, of reference. Markers other than vertical lines may also be produced. Furthermore, by providing a plurality of circuits such as 14, for generating slow ramps of different periods, simultaneous waveform displays may be generated at different rates. Other modifications may also be made in the circuit display.

lclaim:

1. An oscilloscope including a. means for producing deflection of the beam of a cathoderay tube in a first direction at a first frequency,

b. means for producing deflection of said beam in an orthogonal direction to said first direction at a second frequency which is low relative to said first frequency,

. means for defining an interval in each second frequency deflection period, the timing of the occurrence of the interval being changed in successive second frequency deflection periods, and

d. gating means for allowing at least one signal to intensity :modulate said beam only during said intervals whereby the waveform of said signal is displayed on the display of said cathode-ray tube.

12. An oscilloscope according to claim 1 including further gating means for gating further signals to form one or more markers on the display during respective selected first frequency deflection periods in each second frequency deflection period.

3. An oscilloscope according to claim 1 wherein a. said means for producing deflection at a second frequency comprises means for producing a first ramp waveform at said second frequency, and said means for defining an interval comprises b. means for producing a further ramp waveform at a substantially lower frequency than said first ramp waveform, means for detecting coincidences of said first ramp waveform with said further ramp waveform, and d. means for generating said intervals in response to said coincidences, the timing of the occurrence of a coincidence changing in successive periods of said second frequency deflection.

4. An oscilloscope according to claim 3 including further gating means for gating further signals to form one or more markers on the display during respective selected first frequency deflection periods in each second frequency deflection period.

.5. An oscilloscope according to claim 4 wherein said further gating means comprises a. means for detecting coincidences between one or more reference signals and said first ramp waveform, and

b. means for gating said further signals in response to the last-mentioned coincidences.

6. An oscilloscope according to claim 1 including means for superimposing each of a plurality of signals to be displayed on a respective direct shift voltage, whereby the waveforms of each of said plurality of signals are displayed on said display separated in said first direction. 

1. An oscilloscope including a. means for producing deflection of the beam of a cathode-ray tube in a first direction at a first frequency, b. means for producing deflection of said beam in an orthogonal direction to said first direction at a second frequency which is low relative to said first frequency, c. means for defining an interval in each second frequency deflection period, the timing of the occurrence of the interval being changed in successive second frequency deflection periods, and d. gating means for allowing at least one signal to intensity modulate said beam only during said intervals whereby the waveform of said signal is displayed on the display of said cathode-ray tube.
 2. An oscilloscope according to claim 1 including further gating means for gating further signals to form one or more markers on the display during respective selected first frequency deflection periods in each second frequency deflection period.
 3. An oscilloscope according to claim 1 wherein a. said means for producing deflection at a second frequency comprises means for producing a first ramp waveform at said second frequency, and said means for defining an interval comprises b. means for producing a further ramp waveform at a substantially lower frequency than said first ramp waveform, c. means for detecting coincidences of said first ramp waveform with said further ramp waveform, and d. means for generating said intervals in response to said coincidences, the timing of the occurrence of a coincidence changing in successive periods of said second frequency deflection.
 4. An oscilloscope according to claim 3 including furthEr gating means for gating further signals to form one or more markers on the display during respective selected first frequency deflection periods in each second frequency deflection period.
 5. An oscilloscope according to claim 4 wherein said further gating means comprises a. means for detecting coincidences between one or more reference signals and said first ramp waveform, and b. means for gating said further signals in response to the last-mentioned coincidences.
 6. An oscilloscope according to claim 1 including means for superimposing each of a plurality of signals to be displayed on a respective direct shift voltage, whereby the waveforms of each of said plurality of signals are displayed on said display separated in said first direction. 